In a mobile (cellular) communications network, (user) communication devices (also known as user equipment (UE), for example mobile telephones) communicate with remote servers or with other communication devices via base stations. In their communication with each other, communication devices and base stations use licensed radio frequencies, which are typically divided into frequency bands and/or time blocks.
Recent developments in telecommunications have seen a large increase in the use of machine-type communications (MTC) UEs which are networked devices arranged to communicate and perform actions without human assistance. Examples of such devices include smart meters, which can be configured to perform measurements and relay these measurements to other devices via a telecommunication network. Machine-type communication devices are also known as machine-to-machine (M2M) communication devices and have been discussed in e.g. 3GPP technical report (TR) 36.888 V12.0.0 titled “Study on provision of low-cost Machine-Type Communications (MTC) User Equipments (UEs) based on LTE” and 3GPP work item document RP-150492 titled “Revised WI: Further LTE Physical Layer Enhancements for MTC”. The contents of both documents are incorporated herein by reference.
MTC devices connect to the network whenever they have data to send to or receive from a remote ‘machine’ (e.g. a server) or user. MTC devices use communication protocols and standards that are optimised for mobile telephones or similar user equipment. However, MTC devices, once deployed, typically operate without requiring human supervision or interaction, and follow software instructions stored in an internal memory. MTC devices might also remain stationary and/or inactive for a long period of time. The specific network requirements to support MTC devices have been dealt with in the 3GPP TS 22.368 standard (version 12.4.0 for Rel-12 and version 13.1.0 for Rel-13), the contents of which are incorporated herein by reference.
For the Release 13 (Rel-13) version of the standards relating to MTC devices, support for a reduced bandwidth of 1.4 MHz in downlink and uplink is envisaged. Thus, some MTC devices (referred to as ‘reduced bandwidth MTC devices’) will support only a limited bandwidth (typically 1.4 MHz) compared to the total LTE bandwidth and/or they may have fewer/simplified components. This allows such ‘reduced bandwidth’ MTC devices to be made more economically compared to MTC devices supporting a larger bandwidth and/or having more complicated components.
Further, the lack of network coverage (e.g. when deployed indoors), in combination with the often limited functionality of MTC devices, can result in such MTC devices having a low data rate and therefore there is a risk of some messages or channels not being received by an MTC device. In order to mitigate this risk and to better support such ‘reduced bandwidth’ MTC devices, it has been proposed to increase the coverage of certain control channels, for example, the physical broadcast channel (PBCH), the physical random access channel (PRACH), and the physical downlink control channel (PDCCH)—or enhanced PDCCH (‘EPDCCH’) in Rel-13. This is achieved by repetition of transmitted signals which can result in increased likelihood that the signal is received successfully (e.g. corresponding to up to 20 dB coverage enhancement). To facilitate such enhanced coverage, each MTC device will need to inform its serving base station of the amount of coverage required (e.g. 5 dB/10 dB/15 dB/20 dB coverage enhancement) to allow the base station to adjust its control signalling appropriately.
However, as LTE system bandwidths are typically larger than 1.4 MHz (i.e. up to 20 MHz), the system bandwidth needs to be divided into a plurality of ‘narrowbands’ (or ‘sub-bands’), each comprising a maximum of six physical resource blocks (PRBs), which is the maximum number of PRBs that a 1.4 MHz bandwidth limited MTC device can use in LTE. For Rel-13, narrowbands also need to meet the following requirements, amongst others:                a set of DL and UL narrow-band(s) needs to be known to UEs;        PRBs in a narrowband need to be aligned with legacy PRB mapping;        frequency hopping over the system bandwidth is not to be used for at least the primary and secondary synchronization signals (PSS/SSS) and PBCH;        at least in coverage enhancement mode, support frequency hopping over the system bandwidth for common messages (such as random access response, paging, MTC system information block(s), and/or the like);        support hopping patterns between narrowbands;        each narrowband must comprise a set of contiguous PRBs (e.g. up to six adjacent PRBs);        at least for TDD, the same set of narrowbands need to be specified for both downlink and uplink; and        narrowbands must not overlap.        